fix: apply cross-model signature sanitization to single requests

Fixes #70 - Gemini thoughtSignature persisting when switching to Claude

Root cause: sanitizeCrossModelPayloadInPlace() was only called for batched
requests, not for single requests. Gemini's thoughtSignature in tool metadata
persisted and caused Claude to reject with 'Invalid signature in thinking block'.

Bumps version to 1.2.8-beta.0

package-lock.json

@@ -1,12 +1,12 @@
 {
     "name": "opencode-antigravity-auth",
-    "version": "1.2.7-beta.1",
+    "version": "1.2.8-beta.0",
     "lockfileVersion": 3,
     "requires": true,
     "packages": {
         "": {
             "name": "opencode-antigravity-auth",
-            "version": "1.2.7-beta.1",
+            "version": "1.2.8-beta.0",
             "license": "MIT",
             "dependencies": {
                 "@openauthjs/openauth": "^0.4.3",

package.json

@@ -1,6 +1,6 @@
 {
     "name": "opencode-antigravity-auth",
-    "version": "1.2.7-beta.7",
+    "version": "1.2.8-beta.0",
     "description": "Google Antigravity IDE OAuth auth plugin for Opencode - access Gemini 3 Pro and Claude 4.5 using Google credentials",
     "main": "./dist/index.js",
     "types": "./dist/index.d.ts",

src/plugin/request.ts

@@ -1110,6 +1110,9 @@ export function prepareAntigravityRequest(
         // Attempts to restore signatures from cache for multi-turn conversations
         // Handle both Gemini-style contents[] and Anthropic-style messages[] payloads.
         if (isClaude) {
+          // Step 0: Sanitize cross-model metadata (strips Gemini signatures when sending to Claude)
+          sanitizeCrossModelPayloadInPlace(requestPayload, { targetModel: effectiveModel });
+
           // Step 1: Strip corrupted/unsigned thinking blocks FIRST
           deepFilterThinkingBlocks(requestPayload, signatureSessionKey, getCachedSignature, true);